Well I was outside of work, outside the security gate, when I saw what I thought was a blackish purple mylar spinning balloon. I would say it was perhaps 500-1000 feet off the ground, but its hard to say, because, well I know this sounds weird, but its shape was hard to make out the closer it got. It looked spherical, and was scintillating, and curiously, the air around it seemed to shimmer - it was hard to see its edge, that's the only way I can describe it. It moved silently from my left, and I was thinking to myself that if it stopped it would have be a UFO. And then, as if it heard my thought, it stopped directly in front of me! I just stared at it, and I had the most curious feeling of being watched, hard to describe, just felt as if it realized I was looking - so I waved at it. It then started to slowly go up into the sky. As it was going up, its color seemed to change to a whitish metallic, almost like sodium. And then, it began to flash. A bright, neon green, then pink, and yellow. It also - sounds weird again - seemed to phase in and out of the air. It would seem to disappear, then I would see one of the flashes, and it would appear again at some distance and disappear. This continued until it was a tiny speck in the sky and then I couldn't see it anymore.

Interesting day.

If you can help me identify what I saw, or let me know if other people have seen similar craft, I would be very appreciative.